Air tightness, or air permeability, refers to the degree to which air can penetrate a building’s envelope – its walls, roof, floor, and other barriers separating the conditioned (heated or cooled) interior from the unconditioned exterior environment. In layman’s terms, it refers to the prevention of unwanted drafts that can occur through tiny cracks and gaps, often around doors, windows, electrical outlets, or the intersections of walls with floors and roofs. The better the air tightness, the fewer drafts and the less energy you lose.

How is air tightness measured?

Air tightness is quantified using a specific diagnostic tool known as a blower door test. In this test, a specialised fan is mounted into the frame of an exterior door, removing air from the building to create a pressure difference between the inside and outside. This pressure difference forces air in through all unsealed cracks and openings, whose rate and location can be detected using smoke pencils, thermal cameras, and manometers. The outcome of the test is represented as air changes per hour (ACH) under a pressure difference of 50 pascals between the interior and exterior.

What is good air tightness?

While the “ideal” air tightness figure can be variable due to factors like the age of a building, architectural design, and local building regulations, generally, a lower ACH number means a more energy-efficient building. For most modern homes, an ACH target of 3 to 5 at 50 pascals is considered reasonable. However, for the highest tier of energy-efficient buildings, such as those meeting Passive House standards, the target is a remarkably low 0.6 ACH at 50 pascals.

Why you need to make your whole home airtight

Air tightness should be a priority for your entire home because:

1. Energy Efficiency: Uncontrolled air leaks allow warm air to escape in the winter and cool air in the summer, causing heating, ventilation, and air conditioning (HVAC) systems to work overtime to maintain the desired temperature. Thus, an airtight home helps in considerable energy savings.
2. Comfort: Air tightness has a direct bearing on the comfort of your living spaces. A drafty house can cause cold spots in the winter and hot spots in the summer, leading to an overall uncomfortable living situation. Enhanced air tightness ensures consistent temperature across all rooms, elevating the comfort level.
3. Indoor Air Quality: Proper air tightness can protect your indoor environment from external pollutants like dust, pollen, and vehicular exhaust, resulting in better indoor air quality.

Which construction system is best for air tightness?

When it comes to achieving superior air tightness, the construction system chosen plays a critical role. Modern building methods, like structural insulated panels (SIPs) and insulated concrete forms (ICFs), are known to offer superior air tightness because they use large, factory-made components that fit together more tightly, with fewer joints and seams where air can leak out. That said, even conventional wood or steel-frame construction can achieve excellent air tightness, provided that careful attention is given to sealing all potential air leakage points during construction.

What is AeroBarrier and how does it fit in?

AeroBarrier is a groundbreaking air-sealing technology that has changed the game when it comes to achieving airtightness. The AeroBarrier process involves pressurising a building with a fog of sealant particles that are carried by the escaping air to leaks, sealing them from the inside out. The result is a highly airtight building, with air leakage levels far below what can typically be achieved with traditional sealing methods. AeroBarrier can reach and seal even the hidden and hard-to-access leaks, making it a crucial tool in the quest for superior airtightness.

Does air tightness affect air quality?

While it is clear that air tightness improves energy efficiency and comfort, its relationship with indoor air quality is more nuanced. On the positive side, an airtight home can prevent the intrusion of outdoor pollutants, like dust, pollen, and vehicle exhaust fumes. However, without proper ventilation, an airtight home can also trap indoor pollutants, such as volatile organic compounds (VOCs) from paints, furniture, or cleaning products, leading to a potentially unhealthy indoor environment. Hence, proper ventilation is critical in airtight homes. Systems like heat recovery ventilators (HRVs) or energy recovery ventilators (ERVs) can provide the necessary ventilation, replacing stale indoor air with fresh outdoor air, while retaining much of the energy used to heat or cool the air, thereby ensuring good air quality without sacrificing energy efficiency.

In conclusion, air tightness is a multifaceted, yet critical, aspect of a comfortable, energy-efficient, and healthy living environment. Achieving it requires careful design, precise construction practices, and innovative technologies like AeroBarrier. At the same time, balancing airtightness with effective ventilation strategies is critical to maintaining a high-quality indoor environment. The confluence of airtightness and ventilation offers a holistic approach towards building a sustainable and healthy home.